Field of the Invention
The invention relates to a vehicle driving assist apparatus for controlling a traveling direction of a vehicle to prevent the vehicle from departing from an end line of a road.
Description of the Related Art
There is known a vehicle driving assist apparatus configured to alert a driver of a vehicle when the vehicle nearly departs to an outside of a road from a road end line such as a line defined by a curb installed next to the road on which the vehicle travels and a boundary line between grass and the road (for example, see WO 2011/064825).
Further, there is known a vehicle driving assist apparatus configured to execute a road end line departure prevention control for applying a steering torque to a steering column of the vehicle, thereby changing a traveling direction of the vehicle to prevent the vehicle from departing from the road end line when the vehicle nearly departs from the road end line to the outside of the road. Hereinafter, this vehicle driving assist apparatus will be referred to as “the conventional apparatus”.
When the conventional apparatus cannot detect the road end line, the conventional apparatus cannot determine whether the vehicle departs from the road end line.
In this case, if the conventional apparatus is configured to estimate a line extended forward from the road end line detected before the conventional apparatus becomes unable to detect the road end line as an estimated road end line which has not been detected by the conventional apparatus, the conventional apparatus can determine whether the vehicle departs from the road end line on the basis of the estimated road end line.
In this regard, an extending direction of the road end line may change from a direction extending parallel to an own vehicle traveling lane corresponding to a lane in which the vehicle travels, to a direction extending toward the own vehicle traveling lane. When the road end line to be detected, extends toward the own vehicle traveling lane, the conventional apparatus may become unable to detect the road end line. When the conventional apparatus becomes unable to detect the road end line and then, estimates the road end line which cannot be detected as described above, the estimated road end line extends across the own vehicle traveling lane.
If the conventional apparatus determines whether the road end line departure prevention control should be executed on the basis of a determination of whether the vehicle departs from the road end line on the basis of the road end line extending across the own vehicle traveling lane, the conventional apparatus may execute the road end line departure prevention control to change the traveling direction of the vehicle though the vehicle does not depart from the actual road end line.
The invention has been made for solving the above-mentioned problems. An object of the invention is to provide a vehicle driving assist apparatus configured to estimate the road end line which cannot be detected on the basis of the road end line which has been detected before the road end line becomes unable to be detected, thereby executing the road end line departure prevention control without executing the road end line departure prevention control unnecessarily.